Incandescent lamp.



UNITED STATES PATENT OFFICE.

E. ELDRED, OF NEW YORK, -N. Y., ASSIGNOR TO THE COMMERCIAL RESEARCH COMPANY, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

INCYANDQESCENT LAMP.

1,140,134.- No Drawing.

To all whom it may concern Be it known that I, BYRON E. ELDRED, a v

I citizen of the United States, residing at tinuation of my 47 7 ,281, filed February 11, 1909, and in part' New York, county of New York, and State of New York, have invented certain new and useful Improvements in Incandescent Lamps, fully described and represented 1n the following specification.

The present application is in part a conapplication, Serial No.

ened, usually by the employment of heat at about 900 C.', and then squeezing the soft glass firmly intocontact with the wires, as

by the application of a clamp. In this Way, the soft glass in maintained in contact with the wires until the glass sets to a hard condition from its soft or plastic state. This plastic state may persist, under certain conditions of strain or pressure, as low as 400 (3., with the lamp glasses now generally used. As the glass and wires are finally brought to normal temperatures, a contraction ofthe glass and wires takes place. In

use, such lamps are subjected to considerable changes of temperature, during. which expansions and contractions of the glass wall and the leading-in wires take place. If a good seal between the wire and glass is not obtained in making the lamp, or if the seal fails during the use of the lamp owing to the expansions and contractions above re ferred to, the lamp is a total loss.

Platinum has heretoforebeen used as a leading in' wire, because it was the only metal combining various characteristics essential to success. Its coefficient of expansion was low as compared'with most other metals, It had a high melting point and therefore would stand the heat of sealing-in. It had a nonoxidizable surface, so that glass would adhere to it and thereby produce a clinging Specification of Letters Patent. Patented M 18, 1915, Application filed December 30, 1 914. Serial No. 879,734.

union. Hence, if, as was generally the case, the lampglass had a coeflicient of expansion slightly below that of the platinum, the union between the leading-in wire and the glass would be maintained during contraction, because of the elasticity of the glass which, on account of its clinging union with the wire, was put under a tensile strain.

Furthermore, the platinum was-a sufliciently good conductor of electricity for the purpose intended and hence could be used in a size small enough to permit sealing with the a glass. There is some difficulty in making a seal where the leading-in wire is too large, becausethe total diametral expansion of the wire unduly strains the glass, unless the coefiicients of expansionof the wire and glass are identical, which is very rarely the case. While other metals of the platinum group had characteristics similar to platinum, the latter was generally employed, because it is a most convenient one to obtain. Platinum,

however, has a number of disadvantages for use as leading-in wires, probably the most important of which is the .fixity or rigidity of its coeflicient'of expansion. That is to 'say, when platinum is to be used leading-in wire, the selection of the type of glass to be used is controlled by the coeflicient of expansion of platinum. Hence, the lampmaker was confined, in his selection of glasses to those having a coefiicient of expansion-as nearly as possible the same as that of platinum. A further disadvantage of platinum was that, owing to its coeflicient of expansion being somewhat greater than that of the glass .usually employed, it must be used only in relatively smaller sizes, as

otherwise its absolute expansion will be greater than the elasticity of the glass can accommodate and leakage of airwould re sult. Furthermore, although platinum will make "a clinging union with glass, if the glass has a coeificient of expansion too much below that of the platinum, the clinging union will be broken during the cooling of the lamp and air permitted to leak around the wire. Also, platinum was relatively weak in the small sizes which it was necessaryto use to obtain a good seal. This weakness of the small wire made its manipulation more diflicult. Finally, platinum (or any of the metals of the platinum group) is expensive, it requiring great care in handling in order to avoid serious losses.

Many attempts have been made heretofore to produce a satisfactory substitute for platinum as a leading-in wire. It has not been possible to select from the elementary metals,

is too low. Where the difiierence between the coefficient of expansion of the metal and that of the glass is too great, a seal cannot be made or cannot be maintained between the is the difliculty of obtaining an alloy of adetermined coefiicient of expansion. That glass and the wire, under the changes of temperature necessarily resulting. Where the conductivity is poor, a wire of larger diameter must be employed, thereby increas ing the difliculties of making the seal. Metals of a low melting point obviously could not beusedowing to the high temperature of the flame employed in sealing-1n. Attempts have been made to use an alloy wire of high melting metal with a coefficient ofi e xpansion the same as that of platinum, or of the usual lampglasses posed to have substantially the same coe cient of expansion s platinum. These wires have not been successfully employed. One of the reasons for failure of such alloy wires is to say, in the commercial manufacture of alloys of high melting metals, the coefficients are supposed to vary according to the pro -portions of the component metals in the alloy. In practice, however, there is a not unimportant variation, probably due to some unrecognized difference in the heat treatment duringth'e manufacture of such 7 wires. -Furthermore, although a wire of this'type can be made with an average coeiiicientof expansion (from normalto sealinga at some temperatures,

in temperatures) about equal to that of the glass with which it is to be used, such wires do not usually expand regularly through the said range of-temperature and consequently, when cooling down, the glass mightbe subjected to a strain sufficient to break its clinging union to the wire. That ,is to say, although the seal might be'perfect at the setting temperature of the glass, and although at normal temperatures, the coefiicients of expansion of the wire and glass would be so nearly alike as to maintain'a satisfactory seal, if such existed at that temperature, yet'at some in:

termediate temperature when co'olingdown .to the normalthe seal would be broken, be-

cause of the considerable difierence in expansions, a't that temperature, between the wire and glass. I

alloy wires was their ready oxidizability,

A further defect of such thus tending to produce'a coating of oxid onthe'wire during the sealing-in process,

film of platinum. Such wires,

which are sugme ias facture and the inherent difficulty of unitingplatinum to such core metals, leaks existed between the core and, platinum coating. While such leaks may have been due to defective methods of manufacture, they were also the result of the use of a core alloy whose ooefiicient of expansion was too high, viz., either thesame as platinum as high expansion lamp'glasses, which were generally assumed to be about the same as platinum. Where the coefficient of expansion ofthe core is substantially the same as' that of platinum, the core and sheath would expand and contract together and therefore there could be no inching efl ect of the sheath onthe core. lence, unless the union between the platinum in every respect, a leak-would be developed;

A further objection to such composite wires was the poor conductivity of the'wire as a whole. As the resistance of core alloys of the nature described is quite high, and as the platinum sheath itself has but a limited or the same and core was perfectcross section, it was necessary to make sealing-in'wires of this type of a larger diameter than a solid platinum wire, so that, as

. a result, the difliculties of obtaining a good seal between the wire and glass were aggravated.

Some attempts have also /been made toproduce a leading-in wire in which-the alloy core was coated with a sheath consisting of platinum alloyed with other metals. These attempts have not been satisfactory, principally for the reason that the alloy core was of such a nature that its coeflicient of expansion ,was the same as or higher than glass, and generally the same as platinum, while the alloy-sheath had a coefiicient of expansion above that of the glass and also above platinum, owing to the high coefficient of expansion of the material alloyed with the platinum. Consequently, the coefiicient of expansion of the composite wire was altogether too-high relative to the glass with which it was to beousedf In some cases,

the methods of manufacture of such compo- 'site wires provided with an alloyed platinum coating was such as to produce a. coating of irregular thickness, so that the coefiicient of expansion of a section of wire taken vfrom one part would be different from another section taken from the same'wire. troduced an uncontrollable variability re-' suiting in the production'of ma'ny' imperfect erally the core was not properly coated at certain points and this exposed core would oxidize rapidly in the completed lamp, thus leaving passages of porous material through which 'the air could leak into the'la-mp.

The purpose of the present invention is to overcome all of the disadvantages hereinbefore referred to. This is done by providing a wire which is highly conductive and therefore may be used in-sizes of relatively sma l'l cross' section, thus reducing the diflic'ulties'of ma'kinga good seal with the glass.- The wire is strong, because it is provided with 'a strong core and therefore -will satistactorily stand the manipulation necessary in usingit. An important and-probablythe basic advantage is the fact that it can be made to have'any required coefficient of expansion 'needed in the lamp business, thus permitting the use of any selected type of lamp-glass. In this way, the lamp manufacturer is at liberty to select -a type'of glass advantageous for various properties other than its particular coefiicient, of expansion.

A most important additional advantage of applicants invention is that the expansion of :the wire is. reasonably regular, be-

tween the normaltemperature and the temperature at which the glass sets from its plastic state. With a wire whose rate of expansion varies considerably from that "of glass at any temperature between the setting temperature of the glass and normal, there is always the danger that the wire will contract so much more than the glass as to pull loose therefrom and thus leave an opening-aroundlthe wire through which the air can leak. This opening may not be closed satisfactorily by subsequent cooling down of the lamp and wire. For this reason, it is important to have a wire whose rate of expansion from the sealing-in temperature to normal is reasonably regular and therefore approximate to the rate of expansion-of the glass through the same range of temperature. The alloy or other core material which it is necessary to-employ in producingv a leading-in wire, has a rate of expansion which departs considerably from that of glass, at temperatures intermediate the normal and the setting temperature of the glass; but-the completed wire of the present invention overcomes this difficulty 'and corrects this variable rate of expansion by the particular sheath employed, as will be more fully explained hereinafter.

"With the above objects in view, the invention comprises an air-tight receptacle, having a wall of vitreous material into which is sealed a leading-in wire having a nickel-iron alloy core whose coeflicient of expansion is materially less-than that of the glass with which it is to be used, this core carrying a sheath of high melting, highconductive material, whose coeiiicient of ex pansion is considerably above that of such glass, the sheath and core being so firmly united that the composite wire will have a coefiicient of expansion longitudinally and transversely, which is a resultant of the coefficients of expansion of the core and sheath respectively.

The core and sheath above defined embody the invention in its preferred and most advantageous, form, but the invention includes, also, leading-in wires formed of other materials and embodying features of the invention, as defined by the claims.

The coefficients of expansion longitudinally and transversely need not be the same,

'butthey-should not be either too much above nor -too muchbelow the glass with which the wire is to be used. If either coefficient of expansion is too much above that of the glass with which the wire is to be used, the wire during the cooling of the lamp will contract so much more rapidly than the glass that it will break loose from the glass and will leave openings throughwhich air can pass to the receptacle. On the other hand, if the coefficient of expansion of the composite wire should be too much below the glass with which it is to be used, the

glass will shrink so strongly against the wire that, for this reason, the glass may be cracked or broken.

When 'the transverse coeliicient of expansion of the composite wire is greater than that of the glass,-a clinging union between the wire-and-glass is necessary in order that leakage may avoided. This results in a tensile strain in the glass around the wire.

If this tensile strain should be too great owingto too great a contraction of-the wire, the clinging union between the wire and glass is broken.

When the transverse coeflicient of expansion of-the composite wire is about the same as that of the glass with which it is to be used, a clinging union is necessary, but, as

there is little or no tensile strain on thr glass, this union need not be very strong. When'the transverse coefiicient of expansion of the composite wire is less than that of the glass with which it is to be used, the glass contracts more rapidly than the wire and hence tightly pinches the wire, so that a compressive strain in the glass around the wire is obtained. In this case, although a clinging union between the glass and Wire is not imperative,'it is no disadvantage.

It will be clear from the above that where. the'conductive exterior sheath of thecomposite wire is of a non-oxidizable material, it can readily be sealed into glass and a satisfactory seal obtained and maintained, even though the coefiieient of expansion of thewire is somewhat above or is equal to or is somewhat below that of saidiglass. Where,

however, the exterior conductive sheath is of material which would oxidize under ordi nary conditions of sealing-in, a clinging union between the wire and glass may not result, under ordinary operations, because of the formation of a layer of oxid on the of some inert or non-oxidizing gas, such as hydrogen, nitrogen, or steam, the latter being particularly convenient when a copper surfaced wire is used, as copper does not oxidize when heated in an atmosphere of steam.

Many methods may be employed in making the wire. For example, the sheath of high-conductive, high-melting material may be united integrally to the nickel-iron core by a weld union produced in accordance with the process described in the United tates patent to Monnot No. 853,716.

While an integral union between the sheath and the core is highly advantageous and results in a wire of great reliability, the invention is not to be limited to a wire made in that way. It is an important feature of the present invention that a satisfactory wire can be produced even where the union between the sheath and core is not of such a nature as to be termed integral. The reason why the weld union is not an absolute necessity is because, by making the core material so that its average coefiicient of expansion from the normal to the sealing-in temperature is distinctly less than the corresponding coeflicient of the glass with which it is to be used, while the corresponding coeflicient of expansion of the sheath metal is distinctly above that of said glass, the sheath metal will contract strongly against the core so that the usual union formed by soldering, hammering, hot swaging, or other wellknown process, will be sufficient to prevent any leakage between the core and sheath.

In making the wire, it is very advantageous to' combine the core and sheath in billet form and then roll and draw or otherwise work the billet down to wire of the desired size, because of the ease of inspection, measurement of constants, and manipulation in working with a large body such as a billet.

It is particularly to be noted that with the present invention the coefficient of expansion of the glass from which the lamp is to be made is the controlling factor. The type of glass to be used having first been se ected and its average coefficient of ex pansion from about zero degree centig'rade ascertained, the constants of the wire may" 1 then be determined.

The proportions of nickel and iron in the core metal are intended to determine the'coefficient of expansion of the core. In practice, it is difficult to obtain commercially a core material of a uniform, predetermined coeficient of expansion. It is supposed that this lack of uniformity in nickel-iron alloy is due to accidental uncontrollable variations in the heat treatment when uniting the constituent metals of the alloy. Since, therefore, billets of nickel-iron alloy, of a uniformcoefficient of expansion, cannot be obtained conveniently on the market, it is an important feature of the present invention that, not withstanding the variations from the desired standard in the core metal, a wire having a substantially uniform coefficient of expansion may be produced by the use of a sheath of the proper thickness, as will be hereinafter more fully explained. A further peculiarity-in the expansion of the core metal is that, if the expansions through the necessary range of temperature be platted, the'curve of such expansions will at some temperatures depart materially from the average coeflicient of expansion from zero to 'the sealing-in temperature at which the glass sets. Hence, it may be said that in general practice, the usual prede termination of proportions of nickel and iron will result only in a fair approximation to the predetermined coefficient of expansion of the core, the variations usually being sufficient to be disadvantageous in practice. By the present invention, this disadvantage may be overcome because the proportion of sheath metal to the core, that is to say, the thickness of the sheath may be readily varied to determine the resultant average coefficient of the vfinished wire. Hence, a core billet of the required compo-, sition may be provided with a sheath metal of high-conductive, high-melting material having a thickness such that the compound billet will give the required average coefficient of expansion. In practice, the thick ness of the sheath metal as first applied may be greater than is necessary. The billet may then be tested as to its coefficient of expansion and the surplus metal of the sheath turned off to the required diameter to give the resultant average coeflicient of expansion which is required. The billet may then be worked down'to wire of the desired size. It will be seen that a great advantage of the invention is that the coefficient of expansion may be controlled in a reliable manner during the manufacture by varying the thickness of the sheath. Furthermore, since sheath metal of the kind necessary in carrying out the invention has a rate of expansion which is fairly uniform and may be considered as rectilinear, the sheath metal tends;

to straighten out the curve of expansion of the core metal and thus produces a composite wire whose curve of expansion does not depart to an injurious extent from the average coeflicient'of expansion required in the wire. It is partly for this reason that a composite wire made in accordance with this invention satisfactorily maintains a seal at,

be distinctly less than that of the glass with which the wire is to be used, in order that the sheath metal will always contract sufficiently onto the core to maintain a reliable union between the sheath and core.

A few specific examples illustrative of the invention will now be given. Assuming that the type of lampglass selected has an average coefficient of expansion of about 89 or 90x10 and that the completed leading-in wire is to have about the same coefficient, a nickel-iron core metal may be selected having a composition of about 38% to 45% nickel. The average coeihcient of expansion of this core would be approximately from 42X 10 to 77 X 10. Such a core may then be provided with a sheath of suitable high-melting, high-conductive material,

such, for example, as silver, copper or gold, which sheath may be applied to the core in any of the well-known ways. When the core has an average coeflicient of expansion of about 42x10, as before suggested, the sheath, if of silver, would be about 65% of the weight of the'entirebillet; if of copper, the sheath would be about 60%; and if of gold, about 75%. The composite billet may be testedto determine its average coeiiicient of expansion, which should be about that, or not much greaterthan that, of the glass with which it is to be used. If it be found that the average coefficient of expansion of the billet is too great, the composite billet may be put in a lathe andsome of the sheath 'm'etal turned off, after which a further test ofthe coefficient may be made. If the coefiicient is 'toolow, a heavier sheath may be supplied tothe core. The proper constants of the billet having been obtained,- the' billet is then worked down to wire of the desired size, and usually to about .006 inche's to .015 inches in diameter, according to the. size of lamp with which it is to be used. It will be obvious from a consideration of the above example that a certain amount of accuracy is required inmaking such wire, in order that its coeflicient of expansion shall not at any time be too greatly above that of the glass. It should not be more than 105% that of the glass with which it is used. Since it is difficult to avoid some variations in different lots of glass, .it'is obvious that in the use of a wire Whose coeflicient is intended to be the same as the glass or to be-within certain limits above the glass with which itis to be used, there is room for mistakes which may result in failures of some lamps, unless careful supervision of the work is maintained at all times. Hence, when such supervision is undesirable, a leading-in wire whose coefficient of expansion is less than that of platinum is safer in practice, and further advantage is obtained by having its average coefiicient" of expansion less than that of the glass with which it is used.

As an example of a lamp provided with a leading-in wire whose average coefiicient of expansion from normal temperatures to the temperature at which the glass sets to the solid state from its softened condition is less than the glass,- the following is submittedas illustrative: With glass having an average coefficient of expansion of, say, 89 10* from common temperatures up to 300 C. (which would probably average about 93x10 up to the softening point of the glass),.the leading-in wire may have an average coefficient of expansion lying between 60x10" and 75x10 for temperatures up to 300 C. With a leading-in Wire of this description, the pressure between the wire and glass in the completed lamp is sufficient to insure a tight joint and at the same time is not sogreat as to cause cracks in the stem 38% nickel. Such a core material will have i an average coefficient of expansion up to 100 C. of about 25X10 Up to 300 C.', its average will be about 42x10; and at the sealing-in temperature, its average: coe cient of expansion will be about 65x10". A billet of this alloy may be provided, by any suitable method, with anouter layeror sheath of copper-.- This layer may then be. turned down in alathe to the exact thickness required to give thedesired resultant coefiicient of expansion, which may be determined by test of the composite billet. The billet may then be drawn or swaged, or

otherwise worked, into wire and annealed.

' It is to be understood that'the above examples are merely illustrative of the inventer. The wire may be drawn down to a di-: ame'ter offrom .006 to .015 inch.

tion, and that it is not to be limited to the said specific examples.

By the terms high-conductive and high electrical conductivity used in this specification and the claims I mean high conductive or high-electrical conductivity relatively to platinum, referring, for instance, to such metals as copper, silver, gold,

and their alloys having an electricalconductivity that is high as compared with platinum.

What is claimed is 1. The combination, with a gas-tight receptacle having a wall of vitreous material, of a composite leading-in wire sealed therein, said wire comprising a core of metallic material havin a coefiic ient of expansion whose averagel om the setting temperature of the glass down to normal is less than that of the glass through the same range of temperatures, said wire having an external metallic sheath consisting of 'metal of high electrical conductivity, said sheath having a coefficient of expansion whose average for the said temperature range is greater than that of said glass, the said sheath being united to the core togive a resultant average coeihcient of expansion of the wire for the said temperature range such that a union may be made and maintained between said sheath and the glass.

2. The combination, with a gas-tight receptacle having a wall of vitreous material, of a composite leading-in wire sealed therein, said wire comprising a core of an alloy of nickel and iron in such proportions as to give the core an average coefficient of expansion, from the setting temperature of the glass down to normal temperature, which is less than that of the glass for the same range of temperature, said wire having an external copper sheath united to the core and of such thickness as to give to the com: plete wire a resultant average coeficient of expansion over the said range, intermediate those of the copper and the particular alloy.

3. The combination, with-a gas-tight receptacle having a wall of vitreous material, of a composite leading-in wire sealed'therein, said wire comprising a core of nickelsteel having a rate of expansion less than that of the glass and an external copper sheath welded thereto and forming the surface of the wire.

4. The combination, with a gas-tight receptacle having a wall of vitreous material, of a composite leading-in wire sealed therein, said wire comprising a core of nickelsteel having a rate of expansion less than that of the glass and an external sheath consisting of metal of the copper class welded thereto and forming the surface of the wire.

5. The combination, with a gas-tight receptacle having a wall of vitreous material,

of a composite leading-in wire sealed therein, said wire having a surface of copper'and a core having a rate of expansion less than that of the glass.

6 The combination, with a gas-tight receptacle having a wall of vitreous material, of a composite leading-in wire sealed there: in, said wire having a surface of high melting base metal and a core having a rate of ex ansion less than that of the glass.

The combination, with a gas-tight receptacle having a wall of vitreous material, of a composite leading-in wire sealed there in, said wire having a surface of metal of the copper class and a core having a rate of expansion less than that of the glass.

8fThe combination, with a gas-tight receptacle having a wall of vitreous material, of a composite leading-in wire sealed therein, said wire consisting of a two-layer composite wire, one such layer being of nickelsteel having a rate of expansion less than that of the glass, and the other layer of high-expansion high melting metal.

9. The combination, with a gas-tight receptacle having a wall of vitreous material, of a composite leading-in wire sealed therein, said wire consisting of reinforced cop er wire, said reinforcement consisting o? a layer of low-expansion nickel-iron alloy.

10. The combination, with a gas-tight receptacle having a wall of vitreous material, of a composite leading-in wire sealed therein, said wire being composed of a layer of copper and another layer of low-expansion nickel-steel in sufficient amount to reduce in, said wire consisting of a shell of metal of high electrical conductivity having its expansion restrained to a point not greater than that of the glass with which it is used, by a core of nickel-steel whose coefficient of expansion is sufficiently less than that of said glass to give a resultant average coefiicient of expansion of the wire not greater than that of said glass.

12. The combination, with a gas-tight receptacle having a wall of vitreous material, of a composite leading-in wire sealed therein, said wire having a surface sheath. of high melting base metal and a core of metallic material, the thermal expansion of thecore and sheath being difl'erent and so proportioned as toproduce a resultant expansion of. the composite wire such as to secure a seal with the glass.

13. The combination, with a gas-tight receptacle having a wall of vitreous material, of a composite leading-in wire sealed there- 111, said wire having a surface sheath of copper and a core of metallic material, the

thermal expansion of the core'and sheath being different and so proportioned as to produce a resultant expansion of the composite Wire such as to secure a seal with the glass. v

In testimony whereof, I have hereunto set BYRON E. ELDRED.

Witnesses:

A. l/VHITE, M. C. MASSIE. 

